Various bone tissue compositions, prosthetic devices and methods for the use thereof in spinal surgery can be found in the prior art. Bone powder has been used in the prior art to fill surgical sites during surgical procedures. For example, a collagen/demineralized bone composition material for use alone or in combination with a prosthetic device for repair of osseous tissue defects is described in U.S. Pat. No. 5,531,791 to Wolfinbarger, Jr.
Another example of bone powder in the prior art can be found in U.S. Pat. Nos. 5,073,373 and 5,484,601 to O'Leary et al. for a flowable demineralized bone powder composition for use in surgical bone repair. The carrier for the '373 demineralized bone is selected from a group consisting of glycerol, monoacetin, diacetin, and mixtures thereof and specific forms of flowable bone powder compositions include cakes, pastes, creams, and fillers. The '601 flowable demineralized bone powder composition utilizes a polyhydroxy compound and/or an ester as the carrier.
U.S. Pat. No. 5,258,043 to Stone discloses a prosthetic intervertebral disc which can be implanted in the human skeleton to act as a scaffold for regrowth of intervertebral disc material. The disc includes a dry, porous volume matrix of biocompatible and bioresorbable fibers which may be interspersed with glycosoaminoglycan molecules. The matrix is adapted to have in vivo an outer surface contour substantially the same as that of a natural intervertebral disc, whereby the matrix establishes an at least partially bioresorbable scaffold adapted for ingrowth of intervertebral fibrochondrocytes.
Conversely in U.S. Pat. No. 4,904,260 to Ray et al. two prosthetic disc capsules are implanted side-by-side into a damaged disc of the human spine to maintain both the height and the motion, including front-to-back bending, of the affected damaged discs. Each prosthetic disc capsule has a bladder enclosing a fluid containing a therapeutic material that is slowly diffusible through a semi-permeable membrane of the bladder.
A spinal implant for use in spinal stabilization is disclosed in U.S. Pat. No. 5,489,308 to Kuslich et al. The implant is described as including a hollow, cylindrical body having external threading and a plurality of openings formed radially through the body in communication with the body interior. The holes are positioned to chip bone into the implant as the implant is rotated.
Another prosthetic device for spinal repair by inserting the same into intervertebral disc spaces after the removal of an intervertebral disc or after a carpectomy is described in U.S. Pat. No. 5,514,180 to Heggeness et al. A spinal stabilization method is disclosed in U.S. Pat. No. 5,015,255 to Kuslich for fusing contiguous vertebrae in a spine and includes the step of forming an access opening into at least a layer of tissue disposed between contiguous vertebrae to be fused. Additional portions of the tissue layer as well as material of the vertebrae body portions are removed to form an enlarged chamber disposed between the contiguous vertebrae. The chamber is at least partially filled with a graft medium.
U.S. Pat. No. 4,440,750 to Glowacki et al. discloses a plastic dispersion of demineralized bone powder and reconstituted native teleopeptide collagen fibers in a continuous aqueous phase having a substantially physiologic pH and ionic strength used to repair or reconstruct bone by injecting or implanting it at the repair or construction site. The dispersion induces osteogenesis at the site.
U.S. Pat. No. 4,501,269 to Bagby discloses a process for immediate stabilization and subsequent promotion of bone-to-bone fusion in a joint where separation of the bones is restricted by surrounding ligaments or other soft tissue. A hole is bored transversely across the joint, and a cylindrical basket is driven into the hole. Stabilization of the joint is achieved by implanting a rigid cylindrical basket which is filled with the bone fragments produced during the boring step.
Another prosthetic implant is disclosed in U.S. Pat. No. 4,834,757 to Brantigan. This implant uses gauge blocks and permanent implant plugs for surgical procedures to support and fuse together adjacent vertebrae in the vertebral column. The implant plugs are rectangular with tapered front ends and tool receiving rear ends. The gauge blocks are smooth faced for removal while the implant plugs have roughened surfaces to grip the vertebrae and provide channels for bone ingrowth.
Other prior art methods of surgical repair using bone particles include methods for surgically taking bone from other anatomical sites in the patient's body to provide bone material to fill the space created surgically between the vertebral bodies. Bone tissue is frequently taken from the patient's iliac or rib, for example, for this autologous transplant procedure and placed in a spinal cage. Alternatively, the autologous bone dust created by drilling is collected and mixed with the patient's own blood to create a paste which is then placed in the cage. In another alternative procedure, animal collagen is mixed with a ceramic material or with bone and then one of these mixtures is placed inside of the cage. Yet another method encountered in the prior art comprises placing allograft bone mixed with glycerol in the cage. A commercially available product known as GRAFTON.RTM. is also used to fill the cage.
These procedures found in the prior art are clinically functional but have several features which make them undesirable for use. First of all they may involve the extra steps of collecting bone from the patient and then mixing this bone with other materials prior to surgical use inside of the patient. Secondly, these procedures may involve a higher risk of adverse reaction with the patient's tissues because of the biochemical differences between some component used in the process such as bovine collagen or glycerol which is mixed with the allograft bone particles. Thirdly, the bone chips used in the spinal cage tend to fall apart presenting problems in filling the cage as well making sure the cage is full of bone product when the cage is inserted in the vertebrae or other bone area. Glycerin or other water soluble carriers for the allograft bone are very rapidly dissolved in the body and allow the bone particles to easily separate and migrate thereby undoing the careful placement of the bone particles within the wound created during the surgery. Any attempt to introduce the dry bone chips directly into a biocompatible metal cage are generally unsuccessful because the bone chips are too small to be retained by the mesh of the cage and instead act as discrete particulate matter and consequently fall out of the cage in an uncontrolled manner. When larger chips are used, they are difficult to hold together and load into the spinal cage. The prior art also contains several bone compositions which have the consistency of a paste, a putty or a semiliquid. The present invention creates a semisolid mass capable of being extruded yet at the same time being capable of retaining the shape of the extrusion orifice.